(1) Field of the Invention
This invention relates to a method of cleaning a container and an apparatus therefor, and to be more specific, the present invention relates to the method of cleaning the container and the apparatus therefor for washing stain off the container which contains all kinds of ink, resinous paint and so on, and for washing dirt off a food container.
(2) Prior Art
For example, a container such as a drum which contains resinous paint and so on, may often be reused to mix or to dilute some kinds of ink, etc. in addition to an original use for containing all kinds of ink or resinous paints and so on to be carried.
In these occasions, the ink, etc. originally contained in a container stains the inside of the container. It sometimes happens that the stains are almost or completely hardened.
In such a case as above, the stains are washed off by using a volatile solvent such as alcohol, toluene, etc. depending on the contents of the container, or by using appropriate cleaning agent. Generally, the stains are removed by scrubbing the inside (Though the outside may be stained, there is almost no problem in achieving the above-mentioned aim of reuse.) of the bottom and the peripheral wall with a brush. However, this kind of handwork requires much time and effort to scrape off hardened resinous paints and so on, wherefore can not meet a requirement to clean handreds of drum containers a day. Furthermore, it has such problems that the volatile solvent itself used to remove the stains is harmful to human body, and that the prevention of explosion has to be considered.
From the above-mentioned point of view, the inventors of this invention considered introducing a technology of using blast, which is harmless and safe, for exfoliation and removal of the above-mentioned paints and so on. In studying this kind of technology of using blast, the inventors noticed the existence of a cleaning method as disclosed in Japanese Patent Publication No. 6-24730.
According to a technology of this method for cleaning a metal mould, melamine resin powder is blasted together with air onto the surface of the metal mould, in order to remove stains of such a moulding material as rubber.
Before the technology became perfected, glass beads, corn powder, walnut powder, etc. had been used as blast materials. However, there were such problems that abraison was severe, exfoliating action was weak, dust control measures had to be taken, and work environment after use of these materials was deterioated. By using melamine resin powder instead of the above-mentioned materials, superior cleaning effect has been obtained without hardly lowering a temperature of the metal mould.
As a blast-method for exfoliation similar to the above-mentioned method, the existence of a blaster, for example, is noticeable in which fine particles used for repainting, etc., is blasted.
According to this technology, fine particles of sodium bicarbonate (NaHCO.sup.3) are blasted to an object by pressurized air, and the shock generated thereby is used to exfoliate hardened resinous paint and the like. A cleaning apparatus according to this technology comprises a pressure tank which contains fine particles of a material, pressurized air, a valve for mixing pressurized air and the fine particles of the materials, and a nozzle from which the mixture of these is blasted, etc.
Use of the above-mentioned melamine resinous powder has a problem that leads to a pollution problem, because it is resin, unless secondary treatment after blast is done, in other words, unless it is collected and treated separately, Therefore, work of exfoliation costs much since cost of collection should be included.
In addition, hardness of the melamine resinous powder is comparatively higher than that of the above-mentioned sodium bicarbonate, wherefore there was a problem that the surface of the object is damaged when the melamine resinous powder is blasted with the pressurized air of 3 kg/cm.sup.2 .about.10 kg/cm.sup.2. The melamine resinous may be used when rough finishing of the object is acceptable. However, there was a problem that is can never be used when the object was a special container made of aluminium alloy or thin steel, the surface was finished like a mirror, ot the object was plated or filmed.
In comparison with the above, use of the above-mentioned sodium bicarbonate is superior is respect that it has a characteristic of water-solublity, it is harmless and can be added in manufacturing process of food, and that hardness of the sodium bicarbonate is comparatively low wherefore softer hit of blast can be obtained compared to the melemine resinous powder.
The inventors of this invention has already proposed in Japanese patent application Nos. 8-292189 and 9-159108, the method and the apparatus for cleaning in which powder of sodium bicarbonate having these advantages is used as a cleaning agent.
The above-mentioned cleaning apparatus is basically so constructed that a cylindrical container (a drum) to be cleaned is rotated at a certain fixed speed with its axis being laid horizontally, a nozzle coming close to and remote away from the inside of the container from which powder of sodium bicarbonate is blasted against the inner surface of the container together with water spray. However, in use of the cleaning apparatus, first, there was a problem that effectiveness of cleaning (accuracy of exfoliation) does not improve by simply raising blast pressure or by increasing or decreasing the volume of use of the powder of sodium bicarbonate per time, in case the container is for ink, paint, or the like and in case the ink, the paint, or the like is hardened or unhardened. Further, since the blast nozzle goes into and out the container which is horizontally laid, the blast nozzle has to be bent. In a structure of the nozzle in which a stream way is formed at the ball joint available on the market, there was the second problem the stream-way becomes narrow because of the bend at the ball joint and the speed of flow of the powder of sodium bicarbonate is lowered.
Therefore, at first, the inventors considered that the effectiveness of cleaning is related to a degree of dryness of the ink to be refoliated, fineness of powder of the sodium bicarbonate, amount of pressured air, and a speed of blast, and carried studies. At the same time, a necessary arises that the blast nozzle of the ball-joint should be improved so that the speed of flow of sodium bicarbonate powder is not lowered.
Secondary, in the above-mentioned apparatus, the function of automatic control of the nozzle was not enough.